1. Field of the Invention
The present invention relates generally to the construction and use of vascular catheters and, more particularly, to vascular catheters having a reduced-size distal tip capable of selectively receiving either a movable guidewire or a work element.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed limbs of the body and coronary blood vessels that feed the heart. When deposits accumulate in localized regions of the blood vessels, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, where a balloon-tipped catheter is used to dilate a stenosed region within the blood vessel; atherectomy, where a blade or other cutting element is used to sever and remove the stenotic material; laser angioplasty, where laser energy is used to ablate at least a portion of the stenotic material; and the like.
In order to more effectively apply such intervention techniques, a variety of vascular imaging devices and methods may be employed. Of particular interest to the present invention, intraluminal imaging catheters having ultrasonic transducers at their distal ends have been employed to produce images of the stenotic region from within the blood vessel.
A number of designs for ultrasonic imaging catheters have been proposed. One approach has been to use a phased-array of discrete ultrasonic imaging transducers at the tip of a vascular catheter. While this approach is advantageous in that it does not require mechanical manipulation of the transducers, it is problematic in that the image quality is limited. Such a phased-array intravascular imaging catheter is commercially available from EndoSonics Corporation, Rancho Cordova, Calif., as the CathScanner I System.
A more promising approach for intravascular ultrasonic imaging employs mechanical rotation of the ultrasonic signal, either by mechanically rotating the transducer itself or by mechanically rotating a mirror, which radially deflects the ultrasonic signal from the transducer. Mechanical rotation generally provides better image quality than use of a phased-array system, but the design of such catheters is problematic since the designs must provide for rotating the transducer and/or an associated mirror at speeds usually in the range from 500 to 2000 rpm. Moreover, the interior blood vessel must be protected from the rotating components, which could cause substantial injury should they come in contact with the blood vessel.
A number of specific designs for mechanical ultrasonic imaging catheters have been described. An early design is illustrated in U.S. Pat. No. 4,794,931, where the mechanical components of the imaging system are located within a housing at the distal end of the catheter. The housing includes a fixed guidewire at its distal tip which is used to position the catheter within the vascular system. While the use of such fixed-guidewire designs can provide excellent image quality, under some circumstances it is desirable to use an "over-the-wire" design where the catheter may be introduced over a separate (movable) guidewire. The use of a movable guidewire offers certain advantages including improved steering capability through branch coronary arteries and elsewhere and easier catheter exchange, e.g. substitution of an interventional catheter after imaging has been completed.
A particular design for an over-the-wire ultrasonic imaging catheter is illustrated in FIG. 1. The catheter includes the catheter body 10 having an exterior catheter lumen 12 attached near its distal end. A rotatable ultrasonic imaging assembly 14 is mounted at the distal end of the drive member 16, and the device may be introduced over a conventional movable guidewire 18, as illustrated. Designs employing parallel lumens are disadvantageous, however, since the width of the distal tip must be sufficient to accommodate both the ultrasonic imaging element and the guidewire. To be able to cross very narrow lesions, the diameter of the catheter should be as small as possible at the distal end. Ideally, the diameter of the catheter in the region of the rotating imaging element should be minimized, preferably including only the imaging element surrounded by a catheter sheath. The requirement of the separate guidewire lumen increases the minimum size, making this design unsuitable for treatment of small blood vessel lesions and preventing passage through conventional guiding catheters.
Designs of the type illustrated in FIG. 1 are commercially available from Medi-Tech, Inc., Watertown, Mass. A design similar to that of FIG. 1 is illustrated in U.S. Pat. No. 5,024,234, the disclosure of which is incorporated herein by reference.
An alternative design for a mechanical ultrasonic imaging catheter avoids the need for a parallel guidewire lumen by providing for exchange of the mechanical imaging components with a conventional guidewire. As illustrated in FIG. 2, such a catheter comprises a single lumen catheter sheath 20 which can receive a drive wire 22 carrying an ultrasonic imaging assembly 24 at its distal end. The catheter sheath 20 may be initially introduced over a conventional guidewire. The guidewire may then be completely removed and replaced with the imaging assembly. While the diameter of the catheter 20 is minimized, the need to exchange the guidewire and imaging components whenever the catheter is to be repositioned is time consuming and disadvantageous. Such catheters are commercially available from Inter-Therapy, Inc., Costa Mesa, Calif.
For these reasons, it is desirable to provide ultrasonic imaging catheters which have a narrow profile in the distal region and which can be introduced over a separate, moveable guidewire. It is particularly desirable for such designs to allow for imaging within the narrow distal region of the catheter without the need to remove the guidewire entirely from the catheter body. In particular, such an imaging catheter should present a width of less than about 5 French, and more preferably less than about 3 French, to facilitate entry into the coronary arteries and even very tight lesions.
An imaging catheter of the type having a reduced profile distal region is the subject of co-pending U.S. patent application Ser. No. 07/930,977, the disclosure of which is incorporated herein by reference. Such a catheter is illustrated in FIG. 3. This catheter 50 includes a flexible catheter body 52 having a distal region 54 and a proximal region 56. The distal region 54 includes a single common lumen 58, which extends from a distal port 60 to a transition region 62. The proximal region 56 includes a first lumen 64 and second lumen 66. The first lumen 64 carries a movable guidewire 68 which, as illustrated, extends from a proximal port 70 through the common lumen 58 and in distal region 54 and out the distal port 60.
Catheter 50 further includes a proximal housing 80 secured to the proximal end of the catheter body 52. Proximal housing 80 includes a lever 82, which is attached to the drive shaft 72, which permits the user to selectively reciprocate the ultrasonic imaging assembly 74 between a retracted position and an extended position. The ultrasonic imaging assembly 74 would normally be utilized only when it is in its extended configuration. It will be retracted when the catheter 50 is being positioned over the movable guidewire 68.
The housing 80 further includes an electrical connector plug 84 for coupling the electrical leads on the drive shaft 72 to the necessary electrical instrumentation for producing the ultrasonic image and a spindle 86 at the proximal terminal end of the drive shaft 72 for coupling to a motor drive, as described hereinabove. Conveniently, rings and commutators (not shown) may be provided in a conventional arrangement to couple electrical leads (not shown) from the transducer (running along or through the drive shaft 72) to the connector plug 84.
The steps for inserting a catheter having a common distal lumen into a blood vessel are illustrated in FIGS. 4-6. Initially, a guidewire 68 is fed into the blood vessel BV so that the distal end lies beyond the region of stenosis S, as illustrated in FIG. 4. After positioning of the guidewire 68, the catheter 50 is introduced over the guidewire by passing the proximal end of the guidewire 68 through distal port 60 and subsequently threading the guidewire through common lumen 58 of distal region 54 and lumen 64 in proximal region 56. The catheter is advanced axially forward within the blood vessel until the proximal region 54 lies within the region of stenosis. After the catheter 50 has been properly positioned, the ultrasonic imaging assembly 74 may be advanced to the position shown in FIG. 5 (or alternatively it may have been in such position while the catheter was being introduced to the blood vessel). After imaging assembly 74 is located near the distal end of lumen 66, guidewire 68 will be retracted in the distal direction until it is removed from common lumen 58 in the distal region and lies wholly within lumen 64 within proximal region 56. Once common lumen 58 is cleared of guidewire 68, ultrasonic imaging assembly 74 may be advanced axially forward into common lumen 58, where it can then be used for imaging in a conventional manner.
At any time during the imaging procedure, the drive shaft 72 can be retracted to once again clear common lumen 58. After clearing the lumen, the guidewire can again be advanced axially forward so that it is available for repositioning the catheter 50. Alternatively, guidewire 68 may be left in place and the catheter 50 withdrawn over the guidewire so that it remains in place for different catheters to be introduced.
Catheters having a reduced profile distal region offer significant advantages over those previously available. The reduced profile distal region allows for entry into narrow and tortuous regions of a patient's vascular system. Additionally, the presence of two lumens in the proximal region allows for quicker and easier repositioning of the catheter.
However, catheters of this type can be improved further. When inserting a catheter as shown in FIG. 3 into a blood vessel over the guidewire, the guidewire may advance into the wrong lumen in the proximal region, i.e., into the lumen containing the imaging core. It would be desirable to provide some means for directing the guidewire into the appropriate lumen.
Second, it would be desirable to seal the catheter at its proximal end and to provide a means for convenient advancement and retraction of the imaging core or other work element within the catheter body. This would be doubly advantageous in that it would prevent the entry of foreign or infectious material into the patient from the proximal end and also shield the rotating parts of the catheter at that end. Such a proximal end seal and means for advancing the work element would be applicable not only to catheters having a reduced profile distal end, but other types of catheters as well.
Finally, although co-pending U.S. patent application Ser. No. 07/930,977 speaks only in terms of imaging, there is no reason why use of the refinements of the present invention should be so limited. The improvements of the present invention could also be included in catheters which use balloon angioplasty devices, laser ablation devices, mechanical cutters, or other interventional devices as an alternative or in addition to an imaging device.